This invention generally relates to an emergency reactor coolant accumulator for an emergency reactor core cooling system in a nuclear power plant and more particularly to an emergency reactor coolant accumulator typically used in a pressurized light water reactor (PWR).
A typical emergency reactor core cooling system conventionally used includes various kinds of hydraulic lines and components such as valves, borated water storage tanks, pipes, pumps, spray nozzles and so on.
An emergency reactor coolant accumulator in which an accumulator tank contains a borated water under pressurization by a compressed gas such as nitrogen gas i one of the most familiar components includes in the emergency core cooling system before-mentioned. A typical accumulator is generally shown in FIG. 10. In the drawing, a tank 1 communicates with a primary reactor cooling loop (not shown) through a water injection line 2 provided with a check valve 3. The accumulator tank 1 also communicates, at an upper region, with a compressed gas supply source (not shown) through a gas inlet line 4 provided with an on-off valve 5. A compressed gas such as nitrogen is introduced into a gas plenum 8 at an upper region when the valve 5 is open, while the valve 5 is kept closed in the normal operation of a nuclear power plant thereby maintaining a pressurized condition of a predetermined pressure in the tank 1.
On the other hand, an emergency reactor coolant such as a borated water is supplied into the tank 1 through a water inlet line 6 when a supply valve 7 is opened and an accumulator borated water 9 is held under such pressurized condition as before-described in the normal operation of the nuclear plant.
In the normal operating condition, a pressure in the accumulator tank 1 is maintained at a predetermined degree lower than that in the primary reactor cooling loop thereby keeping the check valve 3 in a closed condition.
If a leakage or breakdown occurs in the primary reactor cooling loop, for example, as a credible accident, a pressure in the primary cooling loop decreases thereby causing the check valve 3 to open. Under such an accidental condition, the accumulated water 9 in the tank 1 is driven, under the pressure of the compressed nitrogen gas, into the primary cooling loop through the water injection line 2 so as to cool a nuclear core in a reactor vessel communicating with the primary cooling loop.
Accordingly, as the accumulator water 9 continues to flow out of the tank in such a manner, the level of the water comes down with the expansion of the gas and a decrease in the pressure thereof. It is desirable to keep the pressure of the gas as high as possible so as to inject a remaining water into the loop without delay when the level of the water 9 comes down near the bottom of the tank 1 and the inlet of the injection line 2. There is a risk, however, that some of the gas may flow out together with the water thereby giving undesirable effects to the cooling of the nuclear core.